The present invention relates generally to photosensitive materials and particularly to a porous glass material which is rendered photosensitive by the introduction of a photosensitive silver and chlorine-containing polyphosphate material into the pore structure thereof.
Photosensitive silver and chlorine-containing polyphosphate materials have recently been described in a copending commonly assigned patent application by C-K Wu, filed Feb. 25, 1981 as Ser. No. 237,853. These materials may be characterized as viscous liquids and/or waxy solids provided by, first, forming a solid or liquid polyphosphate condensation product by condensing a mixture of KH.sub.2 PO.sub.4 and AG.sub.3 PO.sub.4 to remove water therefrom, and, secondly, reacting the condensate thus provided with dissolved NaCl to provide the photosensitive polyphosphate.
Photosensitive polyphosphates produced in accordance with the above-described application are intended to be useful in combination with porous support materials such as paper, cloth or the like, and can be applied thereto simply by physically impregnating the porous support with the polyphosphate and removing residual material therefrom. The resulting impregnated support exhibits good photosensitivity in ultraviolet, blue and even green light, such that visible images can be directly produced by exposure of the supported material without any need for chemical or physical development.
However the permanence of this medium is somewhat less than might be desired due to the comparatively fragile nature of paper and cloth support materials. Thus a photosensitive medium incorporating a photosensitive polyphosphate but exhibiting substantially improved physical durability would be desirable.
Porous glasses exhibiting good chemical and physical durability are known. For example, U.S. Pat. No. 2,106,744 to Hood et al. describes the manufacture of a durable porous glass product utilizing a process wherein a phase-separable alkali borosilicate glass is heated to cause phase separation into a major siliceous matrix phase and a minor interconnected thread-like phase rich in boron and alkali. This minor phase can be removed from the glass by leaching in acid to provide a porous glass product consisting of the siliceous matrix. Glasses of this type are referred to in the art as 96% silica glasses because they consist of about 96% silica by weight. They may be used in the porous condition or consolidated by heating to a non-porous state.
Attempts to incorporate the aforementioned newly discovered photosensitive polyphosphate materials into porous glasses such as above described have not been successful. The average pore size of 96% silica glasses produced in this manner is very small, on the order of 40-50 A, and no method has been found by which sufficient photosensitive material can be worked into the microscopic pore structure to provide a photographic image of acceptable optical density upon exposure to light.
The advantages of a photosensitive porous glass material which could be treated to provide photographic images without chemical or physical development would be substantial. An image produced in such a glass could be quite permanent, resisting damage from physical abrasion in use. In addition, as in the case of the less durable supports, the image could be fixed by removing unexposed material from the pores via washing or the like, so that a permanent image resisting change upon subsequent exposure to light could be provided. If necessary, the image could be further protected from change by applying a protective coating or layer to the surface of the porous glass.